Refrigerator construction

ABSTRACT

Disclosed herein is a composite structure for use in thermal insulation panels, especially those panels used in refrigerator cabinets. The composite structure comprises a layer of a gas filled cellular insulation material combined with a layer of impact resistant thermoplastic sheet material, wherein a film of a rubber modified high nitrile polymer containing at least 45% by weight of nitrile monomer units (calculated as acrylonitrile) is interposed between the gas filled cellular material and the thermoplastic sheet. The rubber modified high nitrile polymer film presents an effective barrier to the gas in the cellular material and provides improved impact strength in the composite while retaining good rigidity of the composite structure.

This is a continuation-in-part of patent application, Ser. No. 535,548,filed Dec. 23, 1974 and now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to refrigerator cabinets which areclassified in Class 312, subclass 314. More particularly, the presentinvention relates to composite structures for use as thermal insulationpanels used in the fabrication of cabinets for refrigerators, freezers,ice boxes, picnic coolers, and the like (hereinafter referred to asrefrigerators).

2. Description of the Prior Art

Thermal insulation panels of the type used in refrigerators usuallycomprise a thermally insulating cellular material laminated to an impactresistant thermoplastic sheet which forms the interior surface of thefood compartment of the refrigerator. The interior surface of the foodcompartment, including the inside of the door, which is presented to thefood stored in the refrigerator, is hereinafter referred to as therefrigerator liner.

In most refrigerator construction, gas filled polyurethane foam is usedas the cellular insulation material and acrylonitrile-butadiene-styrene(ABS) polymer or rubber modified polystyrene is used as the refrigeratorliner. The gas found in the cells of the insulation material is usuallya halogenated aliphatic or cycloaliphatic hydrocarbon. These gases arepresent in the cells of the insulation material as residual blowingagents. Alternately, they are incorporated into the cells by design inorder to improve the thermal insulation properties of the cellularmaterial. Examples of these hydrocarbons include trichlorofluoromethane,dichlorodifluoromethane, 1,1,2-trichloro-1,2,2-trifluoroethane, andmixtures thereof.

The composites described above have found widespread use in refrigeratorapplications. Unfortunately, these composites suffer from a disadvantagein that the food liner becomes less impact resistant and moresusceptible to cracking when bonded to the gas filled foam. The loss ofimpact resistance and the tendency to crack is reduced by the use of anelastomeric layer between the gas filled foam and the food liner astaught in U.S. Pat. No. 3,563,845 to J. Stevens. In U.S. Pat. No.3,565,746, the same patentee teaches the use of two different layers ofgas filled cellular material, which layers differ in density andcompressive modulus in order to minimize loss of impact strength. Othermethods used in the art to preserve the impact strength of the ABS layerinclude the use of a wax layer or a layer of polyethylene between thecellular material and the ABS.

The methods described above provide some improvement in the retention ofimpact resistance of the ABS refrigerator liners upon being laminated tothe gas filled cellular material.

However, the impact resistance of the ABS refrigerator liners may stilldeteriorate due to the aging of the elastomeric or wax layers which areinterposed between the cellular material and the ABS food liner. Inaddition, the halogenated hydrocarbons in the cellular material maypermeate the elastomeric, wax and polyethylene layers and attack the ABSsheet surface. In either event the result is a decrease in impactstrength of the ABS sheet in the composite structure.

While the use of wax or polyethylene interlayers between the foam andABS sheet will eliminate stresses and strains which are formed in theABS by virtue of being laminated to the foam, they give rise to anotherproblem. The wax and polyethylene layers provide total release of theABS from the foam and as a result the ABS food liner of the refrigeratortends to lose rigidity and may flex back and forth upon contact. Thisloss of rigidity may be avoided by the use of an adhesive layer whereinthe wax coating or the polyethylene is bonded to both the urethane foamand the ABS sheet, however, this, in turn, gives rise to additionalmanufacturing steps and expenses.

Another disadvantage of the methods used in the prior art is that theelastomeric, wax or polyethylene components must be separated from theABS material in order to recycle any ABS trimmings, scraps, etc.generated in the manufacturing operations back into food liner use as ithas been found that the physical properties of the ABS food linercomponent become less desirable when they are contaminated with minoramounts of the above material. This gives rise to further manufacturingsteps if the trimmings are to be recycled for food liner applications.

A need exists in the art for improved thermal insulation panels forrefrigeration applications wherein the ABS refrigerator liner isprotected against the halogenated hydrocarbons found in the cellularinsulation material used in refrigerator application while maintainingrigidity and impact strength.

SUMMARY OF THE PRESENT INVENTION

The present invention relates to an improved refrigerator cabinetcomprising an exterior surface, a sheet of ABS which forms the interiorsurface of the refrigerator, and a layer of a gas filled cellularinsulation material which is interposed between the exterior surface andthe ABS sheet, wherein the improvement which comprises using an ABSsheet which has bonded thereto a co-extensive film of a rubber-modifiedhigh nitrile polymer wherein the rubber-modified high nitrile polymer isfacing the exterior surface and is in laminated contact with the foam inthe refrigerator cabinet wherein the rubber-modified high nitrilepolymer film contains from 45 to 85 percent by weight, based on thetotal polymer weight, of a nitrile monomer unit and from 5 to 30 percentby weight of a synthetic or natural rubber component, wherein the weightpercent is based on the total weight of the rubber modified high nitrilepolymer.

The present invention also relates to refrigerator cabinets prepared bythe above process.

The nitrile polymer layer presents a barrier to the halogenatedhydrocarbons found in the cellular material and minimizes thedegradation of the thermoplastic ABS sheet material by the halogenatedhydrocarbons. Moreover, the rubber modified nitrile polymer provides arelease surface between the cellular material and the ABS sheet materialwhich results in improved impact resistance in the composite.

DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross section of a composite wherein an ABS sheet 1is bonded to a rubber modified high nitrile polymer 2.

FIG. II illustrates a cross section of a composite prepared from an ABSsheet 1 which is bonded to a rubber-modified high nitrile polymer 2which in turn is bonded to a layer of thermally insulating foam 3.

FIG. III illustrates a cross section of a refrigerator cabinetcomprising an exterior surface 4, a thermally insulating foam 3, whichis bonded to a composite of a rubber modified high nitrile polymer film2, which in turn is bonded to a sheet of ABS 1, wherein the ABS sheet 1forms the interior surface of the refrigerator, i.e., the refrigeratorliner. Also illustrated is a shelf support 5 formed into the highnitrile polymer/ABS composite. In foaming-in-place operations of thetype used in refrigerator construction, such indentations (orproturberances depending on the point of view) may form a trap for thehalogen hydrocarbons 6 used in the foaming operations.

FIG. IV illustrates a conventional refrigerator construction with theABS sheet 1 on the interior of the refrigerator, i.e., the side walls,top and bottom panels and the inside of the door.

FIG. V illustrates a cutaway view of the refrigerator of FIG. IV alongline 5--5 showing a cross section view of the exterior surface 4, thefoam insulation 3, the rubber modified high nitrile polymer 2 and theABS liner 1.

FIG. VI illustrates a conventional picnic cooler construction. The ABSsheet 1 used in the inside of the lid 1 has a corrugated surface whilethe ABS sheet 1 for the interior walls is smooth.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A -- THE FOAM COMPONENT

Normally, the preferred cellular material used as the thermal insulationin the composites of the present invention is polyurethane foam,although other similar cellular material can be used. The halogenatedaliphatic or cycloaliphatic hydrocarbons found in the cells are theresidue of blowing agents or else are deliberately placed in the cellsto enhance the thermal insulation properties of the cellular material.Examples of these halogenated hydrocarbons includetrichloromonofluoromethane, dichlorodifluoromethane,monochlorotrifluoromethane, monobromotrifluoromethane,tetrabromotrifluoropropane, monochlorodifluoromethane,trichlorodifluoroethane, trichlorotrifluoroethane,dichlorotetrafluoroethane, tetrachlorodifluoroethane, etc. Mixtures ofthe foregoing halogenated hydrocarbons are also used.

B -- THE ABS SHEET COMPONENT

The thermoplastic sheet material which forms the food liner portion ofthe composite is an acrylonitrile-butadiene-styrene (ABS) polymer whichcontains from 5 to 40% by weight of acrylonitrile, from 5 to 30% byweight of butadiene and from 30 to 90% by weight of styrene based on thetotal weight of the ABS polymer. The expression ABS is used in thegeneric sense and includes the known equivalents for acrylonitrile(e.g., methacrylonitrile, propacrylonitrile), butadiene (e.g., isoprene,chloroprene, etc.), styrene (e.g., alpha-methylstyrene, halostyrene,etc.). Preferably, the ABS sheet is a high gloss, high impact materialof the type conventionally used in refrigerator construction. The ABSsheet materials used to prepare the thermoplastic sheet component of thethermal insulation panels of the present invention are well known tothose skilled in the art. These materials are described at length inU.S. Pat. Nos. 3,563,845, 3,565,746, 3,509,237, and Belgian Pat. No.803,853, all of which are incorporated herein by reference.Consequently, no further description of these well known ABS materialsis required here.

C -- THE RUBBER MODIFIED HIGH NITRILE POLYMER COMPONENT 1. -- IN GENERAL

The rubber-modified high nitrile polymer used in the present inventioncontains at least 45% by weight of a nitrile monomer unit, based on thetotal polymer weight, wherein the weight percent of nitrile monomer iscalculated as acrylonitrile. More particularly, the rubber-modified highnitrile polymer contains from 45 to 85% by weight of a nitrile monomer.Preferably, the polymer contains 50 to 75% by weight of a nitrilemonomer (calculated as acrylonitrile).

The preferred high nitrile polymers, which are rubber modified for usein the present invention, are polymers of a nitrile monomer and at leastone comonomer. The preferred comonomers which are interpolymerized withthe nitrile monomers include monovinylidene aromatic hydrocarbonmonomers such as styrene, alpha-methyl styrene, halostyrene, etc.; loweralpha olefins containing from 2 to 6 carbon atoms such as ethylene,propylene, butylene, isobutylene, etc.; acrylic acid and methacrylicacid and the corresponding alkyl acrylate and alkyl methacrylate esterswherein the alkyl group contains from 1 to 4 carbon atoms such as methylacrylate, ethyl acrylate, propyl acrylate, butyl acrylate and thecorresponding methacrylates; vinyl esters such as vinyl acetate; alkylvinyl ethers wherein the alkyl group contains from 1 to 4 carbon atomssuch as methyl vinyl ether, ethyl vinyl ether, etc., and mixtures of theforegoing.

The high nitrile polymers used in the present invention contain from 5to 30% and more preferably from 7.5 to 20% by weight of a synthetic ornatural rubber component such as polybutadiene, polyisoprene, neoprene,nitrile rubbers, acrylate rubbers, natural rubbers,acrylonitrile-butadiene copolymers, ethylene-propylene copolymers,chlorinated rubber, etc., which is used to strengthen or toughen thehigh nitrile polymer layer. The percent rubber referred to above is thatof the rubber (ungrafted basis) based on the total weight of the rubbermodified high nitrile polymer composition.

The rubber component may be incorporated into the high nitrile polymerby any of the methods which are well known to those skilled in the art,e.g., direct polymerization of monomers, grafting the nitrile monomeronto the rubbery backbone, polyblend of a rubber graft polymer with amatrix polymer, etc.

2 -- RUBBER-MODIFIED HIGH NITRILE POLYMERS OBTAINED BY GRAFT TECHNIQUES

The preferred method for incorporating a rubber component into the highnitrile polymers of the present invention is by grafting the rubbersubstrate with a monomer mixture to form a graft polymer comprising asuperstrate polymer grafted onto the rubber substrate as is described inU.S. Pat. No. 3,426,102. The graft polymer component is then used aloneor blended with a high nitrile polymer component (the matrix polymer) toform the rubber modified high nitrile polymer. The nitrile content ofthe outer shell of the superstrate polymer should be at least 40% byweight based on the weight of the superstrate when the grafted polymeris to be blended with a matrix polymer in order to provide goodcompatibility and adhesion of the grafted polymer to the matrix polymer.Preferably, the superstrate polymer grafted on the rubber substrate issimilar in composition to that of the high nitrile matrix polymer withwhich it is blended to form the resulting rubber modified high nitrilepolymer.

The rubber substrate onto which the monomers are grafted are dienerubbers or mixtures of diene rubber, i.e., any rubbery polymers (apolymer having a second order transition temperature less than 0°Centigrade, preferably less than -20° Centigrade, as determined by ASTMTest D-746-52T) of one or more conjugated 1,3-dienes, e.g., butadiene,isoprene, piperylene, chloroprene, etc. Such rubbers includehomopolymers and interpolymers of conjugated 1,3-dienes with up to about45 percent by weight of one or more copolymerizable mono-ethylenicallyunsaturated monomers, such as monovinylidene aromatic hydrocarbons(e.g., styrene, halostyrene, alpha-methylstyrene, etc.); ethylenicallyunsaturated nitriles such as acrylonitrile, methacrylonitrile; alkylacrylates (e.g., methyl acrylate, butyl acrylate, 2-ethylhexyl acrylate,etc.); the corresponding aklyl methacrylates; acrylamides (e.g.,acrylamide, methacrylamide, N-butyl acrylamide, etc.); unsaturatedketones (e.g., vinyl methyl ketones, methyl isopropenyl ketone, etc.);alpha olefins (e.g., ethylene propylene, etc.); pyridines; and the like.

A preferred group of butadiene rubbers are those consisting essentiallyof 65 to 100 percent by weight of butadiene and/or isoprene and up to 35percent by weight of a monomer selected from the group consisting ofstyrene, acrylonitrile, methacrylonitrile and alkyl acrylates andmethacrylates, wherein the alkyl group contains from 1 to 4 carbon atomsand mixtures of the foregoing. Particularly advantageous substrates forpreparing polymer blends are interpolymers of 90 to 70 percent by weightbutadiene and 10 to 30 percent by weight styrene.

The average particle size of the rubber substrate prior to grafting mayvary from as little as 0.01 micron to as large as about 10.0 microns,and preferably about 0.08 to 2.0 microns for optimum benefit to impactproperties.

As will be readily appreciated, the ratio of the grafted polymersuperstrate to the rubber substrate may vary widely and is generallywithin the range of 0.1 to 2.0 parts by weight of rubber substrate. Thepreferred composite graft copolymers have a superstrate:substrate ratioof about 0.1 to 1.6:1.0.

3 -- THE MATRIX POLYMER

The preferred polymers used as the matrix polymer, which is blended withthe grafted rubber component to form the rubber modified high nitrilepolymers used in the present invention, are those nitrile polymerscontaining from 55 to 85 percent by weight, based on the total polymerweight, of a nitrile monomer selected from the group consisting ofacrylonitrile and/or methacrylonitrile (wherein the weight percent ofmethacrylonitrile is calculated as acrylonitrile and from 15 to 45percent by weight of at least one comonomer selected from the groupconsisting of monovinylidene aromatic hydrocarbon monomers and alkylester of acrylic and methacrylic acid where the alkyl group containsfrom 1 to 4 carbon atoms and mixtures thereof.

When acrylonitrile is used as the sole nitrile monomer, the preferredrange is from 60 to 83 percent by weight, based on the weight of thematrix polymer of acrylonitrile, whereas with methacrylonitrile thepreferred range is from 70 to 98 percent by weight of methacrylonitrilewhich corresponds to about 55 to 78 percent by weight of nitrile monomercalculated as acrylonitrile. The preferred monovinylidene aromatichydrocarbon monomers are styrene and alpha-methylstyrene while thepreferred alkyl esters are methyl acrylate, ethyl acrylate and methylmethacrylate.

In addition, the graft polymers and matrix polymers described above maycontain up to 10 percent of an additional monomer as for example, loweralpha olefins containing 2 to 6 carbon atoms such as ethylene,propylene, butylene, isobutylene, etc.; vinyl esters such as vinylacetate; alkyl vinyl ethers wherein the alkyl group contains from 1 to 4carbon atoms such as methyl vinyl ether, ethyl vinyl ether, etc., andmixtures of the foregoing.

The amount of the matrix polymer and grafted rubber used in the presentinvention depends on the rubber level desired in the blend, the degreeof grafting onto the rubber substrate, and the relative amounts ofnitrile monomer in each. In general, the amount of the matrix polymerand grafted rubber used is selected to provide a rubber modified highnitrile polymer with a nitrile content of from 45 to 85 percent byweight, preferably 50 to 75 percent by weight, and a rubber content inthe range of from 5 to 30 percent by weight and more preferably from 7.5to 20 percent by weight based on the total weight of the rubber modifiedhigh nitrile polymer, i.e., grafted rubber and matrix polymer.

4 -- RUBBER MODIFIED HIGH NITRILE POLYMERS OBTAINED BY TWO STEP GRAFTINGTECHNIQUES

The especially preferred rubber modified high nitrile polymer componentused in the composites of the present invention are the two stagegrafted rubbers which are taught in U.S. Pat. No. 3,671,607 to Lee etal., and in U.S. Pat. Nos. 3,900,528 and 3,900,529 to L.A. Beer, whichare incorporated herein by reference. Especially preferred rubbercomponents are prepared from butadiene-styrene rubbers having abutadiene content of from 60 to 80 percent by weight, a particle size inthe range of from 0.06 to 0.2 micron before grafting, a gel content inthe range of from 40 to 95 percent and a swelling index in the range offrom 10 to 40. These especially preferred rubbers are grafted in twostages using a first and second polymerizable monomer composition.

The first polymerizable monomer composition grafted onto the rubbercomprises (1) from 0.1 to 2 percent by weight, preferably 0.1 to 1percent by weight, of a nonconjugated diolefin monomer, (2) from 0 to 30percent by weight of an ethylenically unsaturated nitrile selected fromthe group consisting of acrylonitrile, and mixtures of acrylonitrile andmethacrylonitrile which contain up to 20 percent by weight ofmethacrylonitrile, (3) from 40 to 60 percent by weight of a vinylidenearomatic hydrocarbon monomer and (4) from 20 to 50 percent by weight ofan alkyl ester of acrylic or methacrylic acid wherein the alkyl groupcontains from 1 to 8 carbon atoms, wherein the percent by weightreferred to above is based on the total weight of the firstpolymerizable monomer mixture.

The nonconjugated diolefins employed in the practice of this inventionare monomers which have two nonconjugated ethylenically unsaturateddouble bonds per molecule, such that at least one double bond reactsreadily causing the diolefin to interpolymerize with the other monomersused in the first polymerizable monomer formulation. Preferably, thesediolefins have two ethylenically unsaturated double bonds with adifferent degree of reactivity or having a crosslinking efficiency ofless than one. These diolefins may be aliphatic, aromatic,aliphatic-aromatic, heterocyclic, cycloaliphatic, etc. Examples ofsuitable diolefins would include divinyl benzene, ethylenedimethacrylate, ethylene glycol dimethacrylate, triethylene glycoldimethylacrylate, tetraethylene glycol dimethacrylate, polyethyleneglycol dimethacrylate, allyl methacrylate, diallyl fumarate, diallylmaleate, vinyl crotonate, and nonconjugated alpha, omega-diolefins of atleast 5 carbon atoms such as 1,4-pentadiene, 1,7-octadiene, etc.Ethylene glycol dimethacrylate is the preferred difunctional monomer.

The monovinylidene aromatic hydrocarbons which are used in thesuperstrate are the same as those discussed above with styrene andalpha-methylstyrene being preferred.

The alkyl esters of acrylic acid and methacrylic acids used in the firstpolymerizable monomer compostion are those wherein the alkyl groupcontains from 1 to 8 carbon atoms, e.g., methyl, ethyl, propyl, butyl,2-ethylhexyl, etc. Examples of such esters include methyl acrylate,ethyl acrylate, butyl acrylate, methyl methacrylate, butyl methacrylate,2-ethyl hexylmethacrylate, etc. The preferred ester is methylmethacrylate. A particularly preferred first polymerizable monomercomposition contains (1) 0.1 to 2 percent by weight of ethylene glycoldimethacrylate; (2) 20 to 30 percent by weight of acrylonitrile; (3) 40to 60 percent by weight of styrene; and (4) 20 to 50 percent by weightof methyl methacrylate; wherein the percent by weight referred to aboveis based on the total weight of the first polymerizable monomer mixture.

The second polymerizable monomer composition contains from 55 to 85percent by weight of an ethylenically unsaturated nitrile monomerselected from the group consisting of acrylonitrile and mixtures ofacrylonitrile and methacrylonitrile which contains up to 20 percent byweight of methacrylonitrile based on the total weight of acrylonitrileand methacrylonitrile.

The second polymerizable monomer composition contains from 15 to 45percent by weight of a monovinylidene aromatic hydrocarbon monomer suchas styrene and alpha-methylstyrene. Up to 10 percent of themonovinylidene aromatic hydrocarbon monomer can be replaced with avinylidene monomer selected from the group consisting of alkyl vinylethers wherein the alkyl group contains from 1 to 4 carbon atoms, vinylesters such as vinyl acetate and alkyl esters from acrylic andmethacrylic acids wherein the alkyl group contain from 1 to 8 carbonatoms.

The preferred vinylidene monomers, which are used to replace up to 10percent by weight of the monovinylidene aromatic hydrocarbon; includemethyl vinyl ether, ethyl vinyl ether, methyl acrylate, ethyl acrylate,butyl acrylate and the corresponding methacrylates, especially methylmethacrylates.

The grafted superstrate contains a total of at least 40 percent byweight ethylenically unsaturated nitrile monomer and the ratio ofgrafted superstrate to substrate is in the range of from 15-200:100.

The percent by weight referred to above in regard to the second monomercomposition is based on the total weight of the monomers in the secondmonomer composition. The above specified rubber particle size, gelcontent, swelling index and second order transition temperature isrequired in order to provide optimum impact properties.

Preferably, the two stage grafted rubbers described above are blendedwith a matrix polymer which contains from 55 to 85 percent, preferably60 to 70 percent by weight, based on the total weight of the matrixpolymer of an ethylenically unsaturated nitrile monomer selected fromthe group consisting of acrylonitrile and mixtures of acrylonitrile andmethacrylonitrile which contain up to 20 percent by weight ofmethacrylonitrile based on the total weight of acrylonitrile andmethacrylonitrile and from 15 to 45 percent of a monovinylidene aromatichydrocarbon monomer of the type referred to above. Up to 10 percent ofthe monovinylidene aromatic hydrocarbon monomer can be replaced with avinylidene monomer as outlined above.

More preferably, the composition of the matrix polymer is substantiallythe same as the composition of the second polymerizable monomercomposition.

D -- THE ABS/RUBBER MODIFIED HIGH NITRILE POLYMER COMPOSITE

Preferably, the ABS sheet and the rubber modified high nitrile polymerare bonded together to form a unitary structure prior to forming thefoam/high nitrile polymer/ABS composite. This may be accomplished bylaminating the ABS sheet to a film or sheet of the high nitrile polymerusing heat and pressure or by using suitable adhesives. Alternately,either the ABS component or the high nitrile component may be meltextruded onto a preformed film or sheet of the other component. Inanother method the ABS and high nitrile polymer components areco-extruded to form a composite. In still another method a solution ordispersion of either the ABS or the high nitrile polymer component isapplied to a preformed film or sheet of the other component followed byremoval of the solvent or dispersion medium. Other methods for formingcomposites will be obvious to those skilled in the art upon reading thepresent specification. The preferred methods are bonding the materialstogether using heat and pressure by extruding one material onto theother by co-extrusion or bi-extrusion methods.

Preferably, the thickness of the ABS component of the composite is inthe range of from 1,250 to 18,750 microns (50 to 750 mils) in order toobtain the desired degree of structural rigidity and impact strength. Inthis regard it should be noted that in refrigerator construction the ABSliner for the doors is about 2,250 to 3,125 microns (90 to 125 mils)thick while the liner for the food compartment is about 5,000 to 7,500microns (200 to 300 mils) thick.

Preferably, the thickness of the rubber modified high nitrile polymercomponent is in the range of from about 12 to 500 microns (0.5 to 20mils). More preferably, the high nitrile polymer component has athickness in the range of from about 12 to 120 microns (0.5 to 5.0 mils)for ease of fabrication when using lamination (heat and pressure),co-extrusion and bi-extrusion methods to form the ABS/rubber modifiedhigh nitrile polymer assembly.

To produce an especially preferred ABS/rubber modified high nitrilepolymer composite suitable for insulating panels that can be vacuumformed and bonded to a polyurethane foam it is preferred to laminate arubber modified high nitrile polymer film having a thickness of from 25to 75 microns to an ABS sheet that is from 2,250 to 7,500 microns thick.

The exact thickness of the ABS sheet or nitrile polymer film depends onthe properties required. For many purposes a high nitrile polymer filmhaving a thickness of from 25 to 50 microns gives sufficient barrierqualities or chemical resistance. However, laminates which need greaterbarrier qualities or greater chemical resistance will require a thickerhigh nitrile polymer film for example having a thickness of from 50 to100 microns (2 to 4 mils) thick and such thicker films are alsodesirable for laminates which are to form very deep drawn formings sincethe films and sheets can become thin in the areas of maximum stretchafter deep drawn forming.

The ABS and rubber modified high nitrile polymer components may beoriented or unoriented. There appears to be no advantage to usingoriented materials and the use of unoriented materials is preferred toavoid any dimensional changes which may occur in the sheet upon loss oforientation during heating and processing while making the ABS/rubbermodified nitrile rubber composite.

The ABS/rubber modified high nitrile polymer composites used in thepresent invention should have a bond strength sufficient to enable thecomposite to maintain its integrity during the refrigerationconstruction operation, e.g., handling, assembly, foaming-in-place andthereafter during the life of the refrigerator without any substantialseparation. The composite should have a bond strength such that a forceof at least 178.6 gms/cm and preferably 357.2 gms/cm is required toseparate the individual components of the composite. These bondstrengths are readily achieved using the methods outlined above.

The composites of the present invention can be of any convenient lengthand width.

E -- THE ABS/RUBBER MODIFIED HIGH NITRILE POLYMER/FOAM COMPOSITE

The foam member of the composite is usually prepared by foaming-in-placetechniques. This involves positioning the ABS/rubber modified highnitrile polymer composites in a suitable jig or mold in a spaced-apartrelationship to the material that forms the exterior portion of therefrigerator, e.g., enamelled steel, wood, plastic, etc. A foamablemixture is then introduced between the ABS/nitrile polymer composite andthe exterior portion of the refrigerator and the foam mixture is thenfoamed-in-place. The resulting foam adheres to the exterior portion andthe rubber modified high nitrile polymer to provide an integralstructure. The foam can be cured by conventional heating methods or byinfrared or microwave heating methods if so desired. The foam bonds tothe internal surfaces of the walls, i.e., the inside of the exteriorportion and the high nitrile surface of the ABS high nitrile polymercomposite during the process and secures them in the spaced relationshipthereby enabling a rigid structure of high strength to be obtained.

The preferred foamable or foaming composition is a polyurethane and thetechnique used for filling the space can be any of the conventionalcompositions and techniques used for filling spaces and voids in-situ.Examples of suitable compositions and techniques are described in "RigidPlastics Foams" by T. H. Ferrigno, published by Reinhold PublishingCorp., second edition, 1967, pages 1--206.

Alternately, the foam can be laminated to the ABS/high nitrile polymercomposite using a suitable adhesives or melt adhesion techniques. Thebond strengths of the foam to the rubber modified high nitrile polymershould be such that the ABS/nitrile polymer foam composite maintains itsintegrity in the refrigeration without any substantial separation of therespective components. The bond strengths of the foam to the rubbermodified high nitrile polymer are in the same ranges discussed above forthe ABS/high nitrile composite. The bond strengths are obtained quitereadily during the foam-in-place operation.

The exterior surface of the refrigerator cabinet may be fabricated froma wide variety of materials. Examples of such materials include metalssuch as steel, enamelled steel, stainless steel, aluminum, wood,plastics and combinations of the above such as decorative plasticoverlays on metal or wood.

The following examples are set forth in illustration of the presentinvention and are not to be construed as a limitation thereof. Unlessotherwise indicated all parts and percentages are by weight.

EXAMPLE 1

This example illustrates a two stage graft polymerization reaction toprepare a rubber modified polymer which is then used to prepare thecomposite structures of the present invention.

A butadiene-styrene (70% butadiene -- 30% styrene) latex, which isfurther characterized as follows:

    ______________________________________                                        Solids             ˜40% by weight                                       pH                 8.5-8.8                                                    Surface tension    68-72 dynes/cm                                             Average particle size                                                                            0.09 to 0.1 micron                                         Gel content        89% to 93%                                                 Swelling Index     12-16                                                      Refractive index n.sub.d.sup.25                                                                  1.5375-1.5395                                              Tg                 < -40° C.                                           ______________________________________                                    

is diluted to 20 percent rubber solids. One percent of sodium laurylsulfate is added to 2,500 parts of the latex which is charged to areactor and heated under nitrogen and with agitation to about 60° C. Anaqueous solution of 1.0 parts of sodium formaldehyde sulfoxylate and asmall quantity of chelated iron is added before graft monomer addition.To this latex is continuously added over a 1 hour period a first monomercomposition of 100 parts acrylonitrile, 200 parts styrene, 100 partsmethyl methacrylate and 4 parts ethylene glycol dimethacrylate. Duringmonomer addition, 1 parts of potassium persulfate in aqueous solution ischarged to the reactor. Stirring is continued during the addition of thefirst monomer composition and is continued for an additional period of 1hour thereafter. Then, 0.8 part of sodium formaldehyde sulfoxylate and0.8 part of potassium persulfate in aqueous solution is added to thelatex and a second monomer composition of 130 parts acrylonitrile, 70parts styrene and 2 parts tert-dodecyl mercaptan is continuously addedto the reactor over a one-half hour period. Towards the end of thesecond monomer composition addition, a solution of 11 parts sodiumlauryl sulfate is charged to the reactor, and agitation and heating arecontinued for about 30 minutes. The latex is then cooled to 25° C. andfive parts of a conventional antioxidant is added to the batch. Thelatex is then coagulated in a hot aqueous magnesium sulfate solution,the coagulum is filtered, washed with water and dried.

The nitrile content of the resulting grafted rubber is about 14.4percent by weight based on the total weight of the polymer formed. Thegraft ratio of rubber substrate to first grafted superstrate to secondgrafted superstrate is about 100:40:20.

The graft copolymer prepared above is blended with a matrix co-polymerof 63 percent of weight acrylonitrile and 37 percent by weight styrenepreviously prepared by conventional suspension polymerization to provideblends with variations in the amount of rubber (calculated on the basisof the rubber substrate) in the polyblend. The rubber graft and matrixpolymers are compounded by extrusion.

EXAMPLES 2 to 6

These examples illustrate the resistance to halogenated hydrocarbonswhich is exhibited by the high nitrile polymer sheet material used inthe present invention.

A conventional ABS sheet containing 23 percent by weight acrylonitrile,10 percent butadiene and 67 percent styrene (available commercially asLUSTRAN Q394, a registered trademark of Monsanto Company) having athickness of about 0.254 cm (100 mils) is laminated to various highnitrile polymeric sheet materials using heat (80° C.) and pressures inthe range of from 3.5 to 5.6 kg/cm² (50 to 80 psi).

The laminates are cut into 5 cm × 5 cm squares and placed over 50 cm³bottles containing 10 to 20 cc of liquid Freon R-11 (a registeredtrademark of E. I. duPont de Nemours & Company). Weights, and in someinstances, adhesive tape, are used to hold the test sample in place overthe vapors. The average exposure area of the laminate to the Freonvapors is 3 sq. cm. The concentration of Freon is the equilibrum vaporpressure of Freon to 25° C. and 50 percent relative humidity air. Theexposure period is 1 week or about 168 hours. Freon is added asnecessary to maintain 10 to 22 cc in the bottles.

At the end of this time the samples are evaluated in order to determinethe effect of the halogenated hydrocarbon vapors on the ABS component ofthe samples. The results of this test are outlined in Table I below:

                                      TABLE 1                                     __________________________________________________________________________    SUMMARY OF EXAMPLES 2 to 6                                                    RESISTANCE OF HALOGENATED HYDROCARBONS                                                High Nitrile                                                                              Halogenated                                               Example                                                                             Polymer Composition(1)                                                                      Hydrocarbon Resistance                                    __________________________________________________________________________    2     None - ABS Control                                                                          ABS slightly swollen and more                                                 brittle than unexposed ABS                                3     Acrylonitrile/styrene                                                                       No Change                                                         63%    37%                                                            4     Acrylonitrile/styrene                                                                       No Change                                                        (63/37) containing                                                            15% rubber                                                             5     Acrylonitrile/methyl-                                                                       No Change                                                        acrylate (˜70/30)                                                       containing about 11%                                                          rubber                                                                 6     Methacrylonitrile/                                                                          No Change                                                        styrene (90/10)                                                        __________________________________________________________________________     (1)Percent rubber is that of the rubber substrate (ungrafted basis) in th     polymer.                                                                 

The rubber modified high nitrile polymer used in Example 4 is thatprepared in Example 1 above. The polymer was prepared by blending 76parts of the matrix polymer with 24 parts of the grafted rubber preparedin Example 1. The resulting rubber modified high nitrile polymer has anacrylonitrile content of 49 percent by weight and a rubber content ofabout 15 percent by weight based on the total weight of the rubbermodified high nitrile polymer. The rubber modified high nitrile polymerused in Example 5 is a grafted polymer commercially available fromStandard Oil of Ohio under the trademark of Barex 210. The high nitrilepolymers used in Examples 2 to 5 have a thickness of about 25 microns (1mil) while in Example 6 the thickness is about 50 microns (2 mils).

The results in Table I above demonstrate the halogenated hydrocarbonresistance of the high nitrile polymer films used. In their absence, theABS is swollen and slightly embrittled when tested by impacting. At thehigh temperatures experienced in foaming-in-place polyurethanesignificantly more attack is expected in those areas of the structurewhere the halogenated hydrocarbon becomes trapped between the foam andthe ABS sheet, e.g., bottom panels, shelf supports and other areaswherein the ABS sheet protrudes into the interior of the refrigerator(see FIG. III).

EXAMPLES 7 to 16

The following examples illustrate the permeability properties of variouspolymeric materials to halogenated hydrocarbons.

The polymeric materials are formed into films from about 25 to 75microns (1 to 3 mils) thick. Permeability is measured on a Park Cellusing the method and apparatus described by W. R. Park, Semimicro GasPermeability Apparatus for Sheet Material, Anal. Chem., Volume 29, pages1897-9 (1957). The halogenated hydrocarbon used indichlorodifluoromethane which is available commercially as Freon 12, aregistered trademark of E. I. duPont de Nemours & Company.

The results of the permeability tests are tabulated in Table II below:

                                      TABLE II                                    __________________________________________________________________________    SUMMARY OF EXAMPLES 7 to 16                                                   PERMEABILITY TESTS                                                                                     Thickness             Permeability                   Example                                                                            Composition         Microns                                                                            Mils Temperature (° C.)(1)                                                              Factor(2)                      __________________________________________________________________________    7    Polyethylene (high density)                                                                       50   2    25          20                                                                50          70                             8    Polyethylene (low density)                                                                        50   2    25          35                             9    Saran               50   2    25          0.1                            10   Polyvinyl Chloride   50-75                                                                             2-3  25          115                                                               50          200                            11   ABS (23% AN)         50-75                                                                             2-3  25          115                                                               50          170                            12   ABS (38% AN)        25   1    50          12                             13   Acrylonitrile/styrene (63/37)                                                                     25   1    25          < 0.1                                                             50          < 0.1                                                             70          < 0.1                          14   Acrylonitrile/styrene (63/37)                                                                     25   1    25          < 0.1                                containing 15% rubber        50          < 0.1                                                             70          < 0.1                          15   Methacrylonitrile/styrene 90/10                                                                   25   1    25          < 0.1                                                             50          < 0.1                                                             70          < 0.1                          16   Methacrylonitrile/styrene/                                                                        25   1    25          < 0.1                                butadiene (90/10) containing 50          < 0.1                                15% rubber                   70          < 0.1                          __________________________________________________________________________      (1)Temperature used for Permeability test.                                   (2)Permeability factor in cc/24 hr./cm.sup.2 micron/(kg/cm.sup.2). Test       equipment used does not measure permeability factors less than 0.1.      

The ABS polymer used in Example 11 contains 23 percent acrylonitrile, 10percent butadiene and 67 percent styrene based on the weight of thepolymer. The ABS polymer used in Example 12 contains 38 percentacrylonitrile, 10 percent butadiene and 52 percent styrene. The rubbermodified acrylonitrile polymer used in Example 14 is the same as thatused in Example 4 above. The rubber modified methacrylonitrile polymerused in Example 16 is a polyblend of a butadiene rubber grafted withmethacrylonitrile and styrene blended with a methacrylonitrile/styrenepolymer matrix. The nitrile content, calculated as acrylonitrile, ofthis sample is 60 percent by weight and the rubber content is 15 percentrubber by weight, both based on the total weight of the rubber modifiedhigh nitrile polymer.

The data in Table II above illustrate the excellent barrier propertiesexhibited by the rubber modified high nitrile polymers used in thepresent invention (Examples 14 and 16) to the halogenated hydrocarbonsfound in cellular material used for thermal insulation in refrigeratorapplications. This barrier property of the rubber modified high nitrilepolymer component of the present invention helps to protect the ABSrefrigerator liner from being attacked by the halogenated hydrocarbonused in the foaming operation.

EXAMPLES 17 to 25

These examples illustrate the impact strength of the various compositeswhich are prepared by laminating various films including rubber modifiedhigh nitrile films to a conventional ABS sheet. The ABS used in therefrigerator liner is a high impact material of the type conventionallyused in refrigerator construction. Specifically, the ABS contains 23percent by weight of acrylonitrile, 10 percent by weight of butadieneand 67 percent by weight of styrene.

The laminates are prepared by extruding the ABS into a sheet andcontinuously laminating the ABS to various films having a thickness inthe range of from about 25 to 50 microns (1 to 2 mils) using atemperature of about 80° C. and nip roll pressures in the range of from3.5 to 5.6 kg/cm². The resulting laminates are then tested for impactstrength using the Falling Dart Impact (FDI) test described in U.S. Pat.No. 3,563,845 which is incorporated herein by reference. The FDI testconducted at 23° C. (73° F.) wherein the laminate is impacted on the ABSrefrigerator liner side to simulate impact conditions normally occurringin refrigerators.

A second set of test laminates is prepared by laminating the ABS/filmcomposites described above to a slab of polyurethane foam having athickness of about 3.8 cm (1.5 inches) to form an ABS/film/foamcomposite. The composite is prepared by placing a 30 cm × 60 cm sheet ofthe previously laminated ABS/polymeric film composite inside an aluminummold (30 cm × 60 cm × 3.8 cm) with the polymer film facing the inside ofthe mold. The mold assembly is then placed in an air oven and heated to40° to 50° C. A foamable urethane composition (General Latex twocomponent Vultafoam 16F-1402) is then injected through a port in themold and allowed to foam-in-place between the mold and the surface ofthe polymeric film component. The foam, when cool, has a density of 30to 45 kg/cu meter (2 to 3 lbs./cu.ft.). When the resulting ABS/polymerfilm/urethane foam composite is cool, it is removed and cut into 10 cm ×10 cm squares for impact testing. These samples are tested for impactstrength using the FDI test on the ABS side of the composite asdescribed above. The impact strength on the foam composites are reportedas percent (%) change in impact as compared with a control sample whichwas not laminated to foam.

The results of the FDI tests on the ABS/film composite and theABS/film/foam composites are tabulated in Table III below.

                                      TABLE III                                   __________________________________________________________________________    SUMMARY OF EXAMPLES 17 to 25                                                                       Falling Dart Impact Test.sup.1                                                        ABS/Film/Foam                                    Example                                                                             Film Composition                                                                             ABS/Film                                                                              % Change                                         __________________________________________________________________________    17    ABS Control - not                                                                            5.8 (42)                                                                              -50 to -80                                             laminated                                                               18    High Density Polyethylene                                                                      3.2 (23-36)                                                                         -70 to -90                                       19    Polyvinyl Chloride                                                                           6.8 (49)                                                                              -70 to -90                                       20    Acrylonitrile/styrene                                                                        1.4 (10)                                                                              no change                                                63%   37%                                                             21    Acrylonitrile/styrene/                                                                       6.1 (44)                                                                              no change                                              Butadiene rubber. From                                                        Example 4 above.                                                        22    Methacrylonitrile/styrene/                                                                   5.5 (40)                                                                              no change                                              butadiene. From Example                                                       16 above                                                                23    Methacrylonitrile/styrene/                                                                   1.9 (14)                                                                              no change                                              butadiene                                                               24    Acrylonitrile/methyl-                                                                        5.5 (40)                                                                              no change                                              acrylate/butadiene                                                            rubber (From Example)                                                         5 above)                                                                25    Acrylonitrile/styrene/                                                                       4.1 (30)                                                                              no change                                              butadiene rubber                                                              (70/20/10)                                                              __________________________________________________________________________     .sup.1 The FDI test results for the ABS/film composites are given in term     of kilogram-meters with the corresponding ft-lbs units in parenthesis. Th     FDI test results on ABS/film/foam composites are given in terms of percen     change as compared to the corresponding ABS/film composites which are not     laminated to foam.                                                       

The rubber modified nitrile polymer film used in Example 23 above isessentially the same as that used in Examples 16 and 22 except that itcontains only 5 percent by weight of a polybutadiene rubber component.The rubber modified nitrile polymer film used in Example 25 is preparedby blending a grafted butadiene rubber and a high nitrile polymermatrix. The film has an acrylonitrile content of 70 percent by weightand a rubber content of 10 percent by weight. The polyethylene film hasa thickness of about 50 microns (2 mils), the polyvinyl chloride has athickness of about 50 to 75 microns (2 to 3 mils) and the nitrilepolymer films have a thickness of about 25 microns (1 mil).

Referring to the FDI test data for the ABS/film laminates, ControlExample 17 shows the excellent impact resistance of ABS sheet which isnot laminated to a polyurethane foam. Examples 21 to 25 illustrate thecomposites of the present invention wherein a rubber modified highnitrile polymer is bonded to the ABS sheet to provide a barrier to thehalogenated hydrocarbons used in the forming of the insulation material.Examples 20 and 23 illustrate the impact resistance of a compositeprepared using a high nitrile polymer with no rubber modification andwith 5 percent rubber, respectively. The impact strength of thecomposite decreases with decreasing amounts of rubber in the highnitrile polymer component.

Referring to the FDI test data for the ABS/film/foam composites, theimpact strength of the ABS component falls off drastically whenlaminated to foam. The loss in impact strength is still severe whenpolyethylene or polyvinyl chloride is interposed between the foam andthe ABS sheet. However, when using a high nitrile rubber modifiedpolymer layer between the foam and the ABS there is no significantchange in the impact strength of the ABS component.

Four rubber modified high nitrile polymer films were prepared fromblends of the grafted rubber polymers prepared in Example 1 above withtwo different copolymers of acrylonitrile and styrene containing 69percent acrylonitrile and 31 percent styrene and 63 percentacrylonitrile and 37 percent acrylonitrile, respectively. The filmswhich contained two different rubber levels (9 percent and 15 percent byweight of rubber, calculated on the basis of the rubber substrate) hasacrylonitrile contents of about 49.1, 53.8, 54.7 and 60.3 percent byweight. The barrier properties and impact properties of these films makethem especially suitable for use in the present invention.

It is apparent from the above that many modifications and changes arepossible without departing from the spirit and scope of the presentinvention.

What is claimed is:
 1. In a refrigerator cabinet comprising an exteriorsurface, a sheet of ABS which forms the interior surface of therefrigerator, and a layer of a gas filled cellular insulation materialwhich is interposed between the exterior surface and the ABS sheet, saidinsulation material having a major amount of its cells filled with ahalogenated aliphatic or cycloaliphatic hydrocarbon, the improvementwhich comprises using an ABS sheet which has bonded thereto acoextensive sheet of a rubber-modified high nitrile polymer wherein therubber-modified high nitrile polymer is facing the exterior surface andis in laminated contact with the foam in the refrigerator cabinetwherein the rubber-modified high nitrile polymer contains from 45 to 85percent by weight, based on the total polymer weight, of a nitrilemonomer unit and from 5 to 30 percent by weight of a synthetic ornatural rubber component.
 2. An improved refrigerator cabinet as inclaim 1 wherein the cellular insulation material is polyurethane foam.3. An improved refrigerator cabinet as in claim 1 wherein therubber-modified high nitrile polymer is prepared from a nitrile monomerselected from the group consisting of acrylonitrile, methacrylonitrile,and mixtures thereof.
 4. An improved refrigerator cabinet as in claim 1wherein the rubber-modified high nitrile polymer is prepared from ablend of a grafted rubber and a matrix polymer containing from 55 to 85%by weight of nitrile monomer units (calculated as acrylonitrile).
 5. Animproved refrigerator cabinet as in claim 1 wherein the rubber-modifiedhigh nitrile polymer is a blend of:A. a matrix polymer which comprisesfrom 60 to 83 percent by weight of acrylonitrile and from 17 to 40percent by weight of at least one comonomer selected from the groupconsisting of monovinylidene aromatic hydrocarbons, lower alpha-olefinscontaining from 2 to 6 carbon atoms, alkyl acrylates and alkylmethacrylates, wherein the alkyl group contains from 1 to 4 carbonatoms, vinyl esters and vinyl ethers, wherein the alkyl group containsfrom 1 to 4 carbon atoms, and B. a grafted diene rubber.
 6. An improvedrefrigerator cabinet as in claim 5 wherein the rubber substrate used inthe grafted rubber component is a polybutadiene rubber containing up toabout 45 percent by weight of at least one copolymerizablemonoethylenically unsaturated monomer selected from the group consistingof styrene, alpha-methylstyrene, acrylonitrile, methacrylonitrile, alkylacrylates and alkyl methacrylates, wherein the alkyl group contains from1 to 4 carbon atoms.
 7. An improved refrigerator cabinet as in claim 1wherein the rubber-modified high nitrile polymer comprises:A. abutadiene-styrene rubbery substrate having a butadiene content of from55 to 100 percent by weight and up to 45 percent by weight based on thetotal weight of the butadiene-rubbery substrate of a comonomer selectedfrom the group consisting of styrene, alpha-methylstyrene,acrylonitrile, methacrylonitrile, alkyl acrylates and alkylmethacrylates, wherein the alkyl group contains from 1 to 4 carbonatoms, wherein the rubbery substrate has a second order transitiontemperature less than -40° C.; and B. a superstrate grafted onto therubbery substrate which superstrate comprises:1. the polymerizationproduct of a first polymerizable monomer composition comprising:a. from0.1 to 2 percent by weight of a nonconjugated diolefin monomer; b. from0 to 30 percent by weight of an ethylenically unsaturated nitrilemonomer selected from the group consisting of acrylonitrile, andmixtures of acrylonitrile and methacrylonitrile which contain up to 20percent by weight of methacrylonitrile; c. from 40 to 60 percent byweight of a vinylidene aromatic hydrocarbon monomer; and d. from 20 to50 percent of weight of an alkyl ester of acrylic or methacrylic acidwherein the alkyl group contains from 1 to 8 carbon atoms, wherein thepercent by weight is based on the total weight of the monomer in thefirst polymerizable monomer mixture; and
 2. a second polymerizablemonomer composition comprising from 55 to 85 percent by weight of anethylenically unsaturated nitrile monomer selected from the groupconsisting of acrylonitrile and mixtures of acrylonitrile andmethacrylonitrile which contains up to 20 percent by weight ofmethacrylonitrile based on the total weight of acrylonitrile andmethacrylonitrile and from 15 to 45 percent by weight of amonovinylidene aromatic hydrocarbon monomer wherein the percent ofweight is based on the total weight of the monomers in the secondpolymerizable monomer mixture;wherein the grafted superstrate contains atotal of at least 40 percent by weight ethylenically unsaturated nitrilemonomer and wherein the ratio of grafted superstrate to substrate is inthe range of from 15-200:100.
 8. An improved refrigerator cabinet as inclaim 1 wherein the rubber-modified high nitrile polymer comprises thegraft polymerization product of acrylonitrile and an alkyl acrylate,wherein the alkyl group contains from 1 to 4 carbon atoms, onto abutadiene rubber substrate.
 9. In a refrigerator cabinet comprising anexterior surface, a sheet of ABS which forms the interior surface of therefrigerator, and a layer of gas filled insulation material which isinterposed between the exterior surface of the ABS sheet, saidinsulation material having a major amount of its cells filled with ahalogenated aliphatic or cycloaliphatic hydrocarbon, the improvementwhich comprises using an ABS sheet which has laminated thereto acoextensive sheet of a rubber-modified high nitrile polymer wherein therubber-modified high nitrile polymer is facing the exterior surface andis in laminated contact with the foam in the refrigerator cabinetwherein the rubber-modified high nitrile polymer is a blend of:A. amatrix polymer which comprises from 60 to 83 percent by weight ofacrylonitrile and from 17 to 40 percent by weight of at least onecomonomer selected from the group consisting of monovinylidene aromatichydrocarbons, lower alpha-olefins containing from 2 to 6 carbon atoms,alkyl acrylates and alkyl methacrylates, wherein the alkyl groupcontains from 1 to 4 carbon atoms, vinyl esters and vinyl ethers,wherein the alkyl group contains from 1 to 4 carbon atoms, and B. agrafted rubber component wherein the rubber substrate used in thegrafted rubber component is a polybutadiene rubber containing up toabout 45 percent by weight of at least one copolymerizablemonoethylenically unsaturated monomer selected from the group consistingof styrene, alpha-methylstyrene, acrylonitrile, methacrylonitrile, alkylacrylates and alkyl methacrylates, wherein the alkyl group contains from1 to 4 carbon atoms,wherein the rubber modified high nitrile polymercontains from 45 to 75 percent by weight of nitrile monomer units andfrom 5 to 30 percent by weight of rubber substrate.
 10. An improvedrefrigerator cabinet as in claim 9 wherein the rubber component is apolybutadiene-styrene rubber grafted with at least one monomer selectedfrom the group consisting of styrene, alpha-methylstyrene,acrylonitrile, methacrylonitrile, alkyl acrylates and alkylmethacrylates, wherein the alkyl group contains from 1 to 4 carbonatoms.
 11. An improved refrigerator cabinet as in claim 10 wherein therubber component comprises:A. a butadiene-styrene rubbery substratehaving a butadiene content of from 55 to 100 percent by weight and up to45 percent by weight based on the total weight of the butadiene-rubberysubstrate of a comonomer selected from the group consisting of styrene,alpha-methylstyrene, acrylonitrile, methacrylonitrile, alkyl acrylatesand alkyl methacrylates, wherein the alkyl group contains from 1 to 4carbon atoms, wherein the rubbery substrate has a second ordertransition temperature less than -40° C.; and B. a superstrate graftedonto the rubbery substrate which superstrate comprises:1. thepolymerization product of a first polymerizable monomer compositioncomprising:a. from 0.1 to 2 percent by weight of a nonconjugateddiolefin monomer; b. from 0 to 30 percent by weight of an ethylenicallyunsaturated nitrile monomer selected from the group consisting ofacrylonitrile, and mixtures of acrylonitrile and methacrylonitrile whichcontain up to 20 percent by weight of methacrylonitrile; c. from 40 to60 percent by weight of a vinylidene aromatic hydrocarbon monomer; andd. from 20 to 50 percent by weight of an alkyl ester of acrylic ormethacrylic acid wherein the alkyl group contains from 1 to 8 carbonatoms, wherein the percent by weight is based on the total weight of themonomer in the first polymerizable monomer mixture; and
 2. a secondpolymerizable monomer composition comprising from 55 to 85 percent byweight of an ethylenically unsaturated nitrile monomer selected from thegroup consisting of acrylonitrile and mixtures of acrylonitrile andmethacrylonitrile which contains up to 20 percent by weight ofmethacrylonitrile based on the total weight of acrylonitrile andmethacrylonitrile and from 15 to 45 percent by weight of amonovinylidene aromatic hydrocarbon monomer wherein the percent byweight is based on the total weight of the monomers in the secondpolymerizable monomer mixture;wherein the grafted superstrate contains atotal of at least 40 percent by weight ethylenically unsaturated nitrilemonomer and wherein the ratio of grafted superstrate to substrate is inthe range of from 15-200:100.
 12. In a refrigerator cabinet comprisingan exterior surface, a sheet of ABS which forms the interior surface ofthe refrigerator, and a layer of a gas filled cellular insulationmaterial which is interposed between the exterior surface and the ABSsheet, and insulation material having a major amount of its cells filledwith a halogenated aliphatic or cycloaliphatic hydrocarbon, theimprovement which comprises using an ABS sheet which has bonded theretoa coextensive sheet of a rubber-modified high nitrile polymer whereinthe rubber-modified high nitrile polymer is facing the exterior surfaceand is in laminated contact with the foam in the refrigerator cabinetwherein the rubber-modified high nitrile polymer contains from 45 to 75percent by weight, based on the total polymer weight, of acrylonitrileand from 7.5 to 20 percent by weight of a butadiene rubber componentwhich is grafted with acrylonitrile and at least one other monomerselected from the group consisting of styrene, alkyl acrylates and alkylmethacrylates wherein the alkyl group contains from 1 to 4 carbon atoms.13. A refrigerator cabinet as in claim 12 wherein the alkyl acrylate ismethyl acrylate or ethyl acrylate.
 14. A refrigerator cabinet as inclaim 12 wherein the nitrile polymer is prepared from acrylonitrile andstyrene.